Apparatus for welding parts to workpieces

ABSTRACT

Apparatus is provided for welding parts to workpieces at a high rate in the order of 250-300 parts per minute. The apparatus includes an arrangement for supplying the parts to the chuck of the welding tool and a mechanical arrangement for co-ordinating the operation of the tool and the part supply. The entire operation of the tool is controlled mechanically including mechanical means for timing the pilot ad welding arcs of the welding cycle.

United States Paten Ehrlich 1 1 June 6, 1972 [54] APPARATUS FOR WELDINGPARTS T0 2,860,231 11/1958 Stone .219/97 WORKPIECES 3,400,239 "9/ 1968Fahrenbach [72] Inventor: Don E. Ehrlich, Avon, Ohio Pfimary Examiner jTruhe v 73 Assignee: TRW Inc., Cleveland, 01110 14mm"! Examiner-Robe"oNeill Attorney-Philip E. Parker, James R. O'Connor, John Todd, Flledl J1970 Hall and Houghton and Gordon Needleman 70 [21] Appl No 10, 5 ABS CTRelated Application Data Apparatus is provided for welding parts toworkpieces at a [62] Division of Ser. No. 563,914, Jan. 26, 1970, Pat.No. high rate in the Order Of 250-300 parts per minute. The ap-3,557,338, paratus includes an arrangement for supplying the parts tothe chuck of the welding tool and a mechanical arrangement for [52] US.CL... ..2l9/98,2l9/97 co-ordinating the operation of the tool and thepart supply. [51] Int. Cl. ..B23k 9/20, 823k 9/22 The entire operationof the tool is controlled mechanically in- [58] Field of Search ..219/97, 98, 99 eluding mechanical means for timing the pilot ad weldingarcs of the welding cycle. [56] References Cited UNITED STATES PATENTS 1Claim, 15 Drawing figures 2,085,049 6/1937 Spire .219/97 PATEN'I'EDJUH s1912 3, 668 363 SHEET 10F 4 'therebetween. When the part 1 APPARATUS FORWELDING PARTS T WORKPIECIE This is a division of copending applicationSer. filed July 8, 1966 now US. Pat. No. 3,557,338

This invention relates to apparatus for welding and particularly forwelding parts to workpieces at a high rate of speed.

In welding parts and specifically studs to workpieces, the part is firstinserted in a chucklof a welding tool and is then moved into contactwiththe workpiece. Power is then supplied to the part and the workpiecewith the part immediately withdrawn from the workpiece to establish apilot arc is retracted to a predetermined position, a main welding arcis effected between the part and the workpiece with the part thenplunged against the workpiece to complete a weld therebetween.

In this type of welding, commonly known as end welding or stud welding,studs usually have been welded to workpieces at a rate of three or foura minute, with the rate increased to seven or eight studs a minute undersome circumstances. l-leretofore, however, the maximum rate at which thestuds could be welded was limited by the time required for the operatorto load the studs in the welding tool chuck, the time required tocomplete the welding cycle, and the ability of the welding power sourceto again reach peak power for another welding cycle after establishingthe pilot and main welding arcs of the last cycle. More recently, withthe development of automatic stud or part feeding systems, and withimproved power sources, small studs have been able to be welded at ratesas high as 50 to 60 per minute.

The present invention relates to apparatus for welding parts at evensubstantially higher rates than those heretofore achieved. The newapparatus is capable of welding studs or parts at continuous rates ashigh as 250-300 per minute. This has been accomplished by unique meansfor operating the welding tool including supplying the parts to bewelded to the tool, moving the tool from a remote, part-receivingposition to a position in which the part is in contact with theworkpiece, and moving the chuck of the tool and the part to be weldedfrom the position in contact with the workpiece to a retracted positionand back again to the workpiece during the actual welding cycle. Theentire operation of the tool is controlled mechanically, includingmechanism for moving the tool between the part-receiving position andthe position in which the part is in contact with the workpiece andmechanism for moving the chuck and the weldable part from the positionin contact with the workpiece to the retracted position during thewelding cycle. In addition, the apparatus includes mechanical means fortiming the pilot and welding arcs and also for feeding a weldable partto the, chuck when the tool is in the remote position. In a preferredform of the invention, the welding tool is moved in an arcuate pathbetween the partreceiving and the welding positions in a manner suchthat the weldable part is provided a slight wiping action as it contactsthe workpiece prior to being welded thereto. This assures an effectiveelectrical contact between the part and the workiece.

p Alsoin accordance with the invention, the welding tool is equippedwith an electrode designed to contact the workpiece and complete acircuit for the welding power. The electrode is spaced from the chuckleg of the tool and is movable independently thereof. Further, the chuckof the welding tool is equipped with a movable stop which enables theweldable parts to be supplied thereto at the extremely high-rates ofwelding achievable with the apparatus. Specifically, the movable stopconstitutes a pivotable gatelocated at the end of a part-receivingportion of the chuck, which gate is springloaded and yields as a part ismoved into and slightly beyond the welding position with respect to thechuck. The movable stop then gently moves the weldable part back to theexact welding position with respect to the chuck. The movable stop thengently moves the weldable part back to. the exact welding positionrelative to the chuck. This assures accurate positioning of the partseven with extremely rapid feeding, with the inertia of the weld-ablepart effectively overcome by the stop.

and with parts in section,

It is, therefore, a principal object of the invention to provideapparatus for rapidly welding parts to workpieces.

Another object of the invention is to provide apparatus for weldingparts to workpieces with the movement of the apparatus and the supply ofweldable parts thereto being controlled entirely by mechanical means.

Still another object of the invention is to provide apparatus forwelding parts at a high rate with a unique chuck for yieldably receivingthe parts to be welded.

-A further object of the invention is to provide apparatus for weldingparts to workpieces with a welding tool moved between a part-receivingposition and the workpiece in an arcuate path, to provide a wipingaction between the part and the workpiece.

Still a further object of the invention is to provide apparatus forwelding studs which includes a chuck leg and an electrode independentlymounted in the same welding tool body.

Other objects and advantages of the invention will be apparent from thefollowing detailed description of a preferred embodiment thereof,reference being made to the accompanying drawings, in which:

FIG. 1 is a view in perspective of overall apparatus embodying theinvention;

FIG. 2 is a fragmentary side view, with parts broken away of amechanical controller and a feeding device of the apparatus of FIG. 1;

FIG. 3 is a sectional view taken generally along the line 33 of FIG. 2;

FIG. 4 is a side view with parts broken away in cross section, of themechanical controller;

FIG. 5 is a vertical sectional view taken centrally through a weldingtool of the apparatus of FIG. 1 and also showing portions of links usedto support and move the tool;

FIG. 6 is a view in vertical cross section taken along the line 6-6 ofFIG. 5;

FIG. 7 is an enlarged rear shown in FIGS. 5 and 6;

FIG. 8 is a view in vertical cross section taken along the line 8-8 ofFIG. 5;

FIG. '9 is a view in elevation, with parts broken away and in crosssection, of components for controlling power supplied to the weldingtool; I

FIG. 10 is a schematic diagram showing the manner in which thecomponents of FIG. 9 are connected to the tool;

FIGS. 11-14 are schematic views in left side elevation of the weldingtool and associated components during a welding cycle when feeding apart to the tool and welding the part to a workpiece, AND

FIG. 15 is a somewhat schematic, fragmentary side view of the feedingdevice of FIG. 2 and further showing a tab stack support of the device.

Referring more particularly to FIG. 1, apparatus in accordance with theinvention is shown specifically as applied to welding opening tabs toscored can lids for the purpose of opening cans to which the lids areapplied without requiring can openers. Can lids to which the tabs arewelded are indicated at 20 and preferably have spiral scores thereon toform opening strips as shown more particularly in a co-pendingapplication of Robert W. Murdock, Ser. No. 491,154. The lids are movedwith a rapid, intermittent motion by a conveyor schematically indicatedat 22 at a rate of 250-300 lids per minute, for example. Opening tabs 24are shown in FIGS. 1, 3, 5, and 8 and are welded to the lids 20 at acorresponding rate of 250-300 welds per minute. The tabs 24 haveprojections 26 (FIGS. 3 and 8) which are welded to end portions of thescored strips on the can lids 20. The tabs also can be equipped withsuitable reinforcing ribs or ridges 28, as shown in FIGS. 3, S, and 8.

The overall apparatus of FIG. I basically includes a drive motor 30, asuitable speed control 32, a mechanical welding controller 34, a weldingtool 36, and a feeding device 38. The welding apparatus can be includedas part of an overall machine which also stamps the lids and tabs. Inthat instance,

and with parts perspective view of the chuck other drive apparatus ofthe overall machine can be substituted for the motor 30 and the speedcontrol 32.

WELDING TOOL The welding tool 36 is shown in more detail in FIGS. and 6.The tool 36 includes a housing 40 slidably carrying a chuck leg 42 bymeans of sleeve bearings 44. The chuck leg 42 is insulated from thehousing by a sleeve 46 which has a groove 48 therein to receive a tang50 of a collar 52 affixed to the chuck leg 42. In this manner, the chuckleg 42 always remains in a fixed position relative to the tool. Thecollar 52 also forms a seat,.along with a shoulder 54 of the insulatingsleeve 46, for a plunge spring 56. The plunge spring urges the chuck leg42 downwardly and outwardly of the housing 40 to the extent permitted byan upper adjustable stop 58. A suitable nut 60 on top of the stop 58provides a terminal connection for a conductor by means of which poweris supplied to the chuck leg 42. The lower end of the chuck let 42 isthreaded to facilitate the attachment of a chuck 62, the details ofwhich will be discussed subsequently.

-A lifting link 64 connects the upper end of the chuck leg 42 to alifting pin 66 of insulating material, relative to which pin the link 64can be adjusted by a separate screw and nut assembly 68. The lifting pin66 extends downwardly through a rear extension 70 of the housing 40 andis efiective to retract the chuck 62 and the leg 42 from the workpieceor can lid when the pin 66 is pushed upwardly by means to besubsequently described.

In most instances, it has been common to connect the power supply to theweldable part by means of the chuck leg and to connect the power supplyto the workpiece by a separate terminal attached thereto. In thisinstance, however, power is supplied to the workpiece through a separateelectrode 72 which can be supported similarly to the chuck leg 42, beingslidably mounted by bearings 74 in a sleeve 76. A collar 78, which canalso have a tang for orienting the electrode if desired, provides oneseat and a sleeve shoulder 80 provides a second seat fora spring 82. Theupper end of the electrode 72 has a stop member 84 and a nut 86threadedly mounted thereon to receive a conductor for supplyingpower-through the leg 72 to the workpiece. An adjustable tip 88 isthreadedly engaged on the lower end of the electrode 72 and is movedinto contact with the workpiece at the same time as the weldable part 24to establish an electrical path from the conductors through the chuckleg 42 and the electrode 72, through the chuck 62 and the tip 88, andthrough the weldable part 24 and the workpiece, when in contact. In thisinstances, when the tabs are welded to steel can lids, the polarity ofthe power preferably is opposite to that normally employed in weldingoperations of this type.

WELDING CHUCK The chuck 62 must be capable of receiving the weldableparts 24 at a rapid rate and securely hold them in the proper position.The chuck 62 includes a magnet 90 of circular cross section threadedlyengaged on the lower end of the chuck leg 42. A chuck block or body 92is affixed to the magnet, as by a press fit, and has a part-receivingportion 94 including a longitudinally extending shallow groove or recess(FIG. 7) to assure clearance for the longitudinal ribs 28 of the tab.The weldable part 24 is fed longitudinally from the rear with a pair ofside' guides 96 and 98 facilitating movement of the tab to thepart-receiving portion 94 of the chuck. When the part is positionedrelative to the chuck, it is held by the magnet 90 during the weldingoperation.

. Being fed to the chuck 62 at rapid rates, the weldable parts haveconsiderable inertia when moved rapidly to the partreceiving portion 94.This renders the parts extremely difficult to control and to positionaccurately relative to thechuck. However, in accordance with theinvention, the problem of proper positioning of the parts is overcome bymeans of a yieldable stop or gate 100 movably supported at the front ofthe chuck. As shown, the gate is pivotally mounted by cars 102 and a pin104 at the front end of the chuck body 92 and the portion 94. The stop100 extends downwardly below the surface of the portion 94 sufficientlyto engage the nose end of the part 24 when moved through thepartreceiving portion and urged slightly beyond the end thereof. Whenengaging the part, the stop swings outwardly slightly as shown in dottedlines in FIGS. 6 and 8 against the force of a spring 106 held undertension between a tab 108 of the stop 100 and a pin 1 10 mounted on thebody 92. The stop 100 thereby brings the weldable part 24 to a stop andthen urges it back to the proper welding position with the nose of thepart aligned with the forward end of the portion 94. The part is thenheld by the magnet 90 until welded to the workpiece, at which time theforce of the magnet 90 is overcome as the chuck is retracted and thepart remains welded to the workpiece.

While the chuck 62 is effective in handling the weldable parts 24,occasionally a part will be dropped from the chuck or the supply ofweldable parts will be exhausted with the result that the chuck willmove downwardly into welding position with no weldable part carriedthereby. In such an instance, the pilot and welding arcs wouldordinarily be struck between the chuck and the workpiece causing burningof the chuck and early replacement thereof. To overcome this, inserts112 and 114 are mounted in the chuck by cutting away portions thereofand by mounting the inserts 112 and 114 therein but separated from thechuck body by insulating layers 116. The inserts 112 and 114 arepositioned in locations such that they are the only portions of thechuck which will contact portions of the workpiece if no weldable partis carried thereby. Being insulated from the body, the inserts willprevent a conducting path from being formed between the chuck and theworkpiece, with the result that no welding arc will be established. Byusing the insulating layers 116 between the inserts 112 and 114 and thechuck block 92. The inserts need not be made of insulating material butcan be of longer wearing metal.

FEEDING DEVICE While the chuck 62 must receive and position the orientedparts rapidly, they must also be fed to the chuck rapidly. For thispurpose, the feeding device 38 includes a block 118 (FIG. 2) which formsa horizontally extending guide passage 120 for a slide 122, and alsoforms a vertical supply passage 124 to receive a stack of the parts 24arranged horizontally and partially nesting with one another in thestack. The slide 122 has a recess or ofiset portion 126 (FIG. 6) toreceive the part 24 and an offset or shoulder 128 which engages the rearend of the lowest part 24 (FIG. 2) and carries it to the chuck 62 as itmoves outwardly in the guide passage 120. The offset portion 126 of theslide 122 preferably is slightly longer than the weldable part 24 andmoves outwardly sufficiently far to cause the part 24 carried thereby toengage the stop and move it outwardly slightly. When the slide retractsto receive the next part, the stop 100 then pushes the newly depositedpart rearwardly slightly to the proper welding position.

The parts and specifically the tabs 24 can be fed to the passage 124 inany suitable manner, as long as they are properly oriented with the noseend toward the welding tool 36. It has been found that if the stack inand above the passage 124 is sufficiently high, it is sometimesdifficult for the slide 122 to engage and push the lowest tab 24outwardly to separate it from the stack. To overcome this, a plunger, tobe discussed subsequently, can clamp an intermediate portion of thestack of tabs and thereby relieve the weight and pressure of thoseabove. Altemately, a blade can be carried by the block 118 and be movedinwardly between two of the tabs.

spaced a few tabs above the lowest one so as to remove the weight of thestack of tabs from the lowest one temporarily.

. the pivot pin 132. pivotally connectedto a supporting shaft. 138rotatably held MECHANICAL WELDING CYCLE CONTROL The operations of thewelding tool 36 and the feeding device 38 must be carefully-and closelycontrolled to-achieve the rapid welding rate. Lack ofcoordinationbetween the various operations of the 'cycle can either extend the cycleunduly long or cause interference and damage of 'the various components.Accordingly, the mechanical controller 34 foraccomplishing thispurposewill now be discussed-in detail.

A. Welding Tool Drive The drive'for the welding tool 36 will bediscussed first; The welding tool body 40h'as a pair of pivot pins 130and 132 (FIG. 5) extending therefrom toward the controller 34. An upperlink 134(FIG. 2 also) is pivotally connected to the pivot pin 130 and alower, curved link 136 is pivotally connected to The opposite end of theupper link 134 is by the controller 34 while the opposite end of thelower link 136 issupported by a rotatable shaft 140 also rotatably heldb'y'the controller 34. The linksl34 and 136 functionally are parallellinks withthe pins 130 and 132 and'the shafts 138 and 140 being equallyspaced and located on parallel lines. As shown, the lower link 136 iscurved only for clearance purposes when in its lower position.

As shown in FIG. 2, an arm 142 is afiixed to'the shaft 138 and, by a pin144, is pivotally connected to a spring rod 146. The rod 146 extendsthrough a passage 148 in a guide and support bar 150 which is pivotallysupported by the sidewalls of the controller 34. A return spring 152 ispositioned around the rod 146 and is maintained under compressionbetween a seat-' ing ring 154 backed up by the bar 150 and a seatingring 156 backed .up by a nut 158 on the end of the rod 146. The spring152 thereby urges the arm 142 and the shaft 138 in counterclockwisedirections so as to urge the welding tool 36 to the upper position.

Referring to FIG. 4, the lower, drive'shaft 140 for the tool 36 has adrive arm 160 affixed thereto with a pivot pin 162 connecting the arm toan intermediate drive link 164. The link 164, in turn, is pivotallyconnected by a pin 166 to an L- shaped drive lever 168. The lever 168has a lower end pivotally supported by a pin 170 with an intermediateportion rotatably carrying a cam follower 172 on a stub axle 174. Thecam follower 172 is urged against aflat cam 176 mounted on a drive shaft178 which is rotated in a clockwise direction by the speed regulator 32to the motor 30. The cam follower 172 is maintained in contact with thecam 176 by virtue of the return spring 152 which urges the shaft 138,and, consequently, the shaft 140 in a counterclockwise direction so asto urge the cam follower against the cam through the intermediate link164.

B. Chuck Drive The above drive arrangement moves the welding tool up anddown between the part-receiving and welding positions. The control forretracting the chuck during an actual welding cycle will now bediscussed. When the welding tool is in the lower, welding position, thelifting pin 66 is engaged by an adju'stable screw 180 (FIGS. 2 and 6) ofa lifting arm 182. The am 182 is mounted on a drive shaft 184 whichextends into the control housing. The shafi 184, as shown in'FIGS. 2 and3, has an intermediate tang 186 affixed thereto which is urged forwardlyby a spring 188 mounted between the upper end of the tang 186 and asuitable seat 190. The lifting arm 182 thereby is normally urged towardits lower position. At the end of the shaft 184 is a drive arm 192(FIGS. 3 and 4) which is engaged by a push rod 194 supported andguidedin a bracket 195 and moved longitudinally by a second, lifting cam'196.The cam 196 has a relatively sharply rising portion 198 which moves therod 194 forwardly to turn the drive arm 192 in a counterclockwisedirection and cause the lifting arm 182 to raise the chuck 62 relativeto the tool body 40 and retract the chuck from the workpiece. The cam196 also has a sharp offset 200 which enables the arm 182 to dropsuddenly by the force of the spring 188 and enables the chuck and aweldable part carried thereby to be plunged back against the workpieceby means of the spring 56. C. Feeder Drive The controller 34 also mustbe capable of operating the feedingdevice 38 to supply a weldable partto the workpiece at the proper-time when the welding tool is in theupper, partreceiving position. For this purpose, the feed slide 122 isconnected bya suitable link*202 and an arm 204 (FIGS. 2 and 3) to a feeddrive shaft 206. An arm 208 is affixed to the shaft 206 within thecontroller and, in turn, is connected through a link 210 to a camfollower lever 212. The lever 212 is pivotally held by an axle- 214extending across the controller and rotatably carries a cam follower 216above the link 210. The opposite end of the lever 212 is pivotallyconnected to a spring rod 218 which extends through a pivot block 220and carries a spring 222 under compression between the block 220 and anouter seating ring 2%. The spring thereby urges the lever 212 inaclockwise' direction and urges the followeror roller 216 against athird, feed cam 226. As the cam 226 rotates, it oscillates the driveshaft 206 and causes the slide 122 to move from a retracted position inwhich it receives the parts to a forward position in which it suppliesthe parts to the chuck, then returning to the first position by means ofthe spring 222.

D. Welding Power Control In accordance with the invention, the power forthe welding cycle is also controlled in part by mechanical means.Referring to FIG. 9, a switch rotor 228 is mounted on the main driveshaft 178 just outside the controller. 34. The rotor 228 carries aconducting sector 230 which conducts electricity and controls suitablewelding circuitry, depending on its position. An annular brush housing231 is mounted on the controller and carries, in this instance, threebrushes or contacts 232, 234, and 236 which contact the outer surface ofthe rotor 228, and the sector 230 when in the appropriate position.

As shown schematically in FIG. 10, as the drive shaft rotates and movesand the sector 230,clockwise,' it first completes a pilot arc circuitbetween contacts 232 and 234 to enable a pilot arc to be establishedbetween the weldable part and the workpiece when in the appropriatepositions through a pilot arc circuit. As the sector rotates further, itelectrically connects the contacts 234 and 236 to establish the mainwelding are between the weldable part and the workpiece through awelding arc circuit. This contact preferably occurs as the stud beginsits plunge stroke. The welding arc is superimposed on the pilot arcsince the contacts 232 and 234 are still electrically connected. Thecontacts 234 and 236 preferably remain electrically connected until atleast the time that the part is plunged back into contact with theworkpiece.

WELDING OPERATION The overall feeding and welding cycle will now bediscussed in more detail. With the chuck 62 in the upper position andthe slide 122 in the rear, partreceiving position, as shown in FIG. 2,the shaft 206 is rotated in a clockwise manner to cause the link 202 andthe arm 204 to move the slide forwardly toward a position immediatelybelow the chuck. As the slide moves forwardly, the offset 128 catchesthe lowermost part from the stack and carries it forwardly to theposition under the chuck, shown in FIG. 11. Actually, the slide iscaused to move slightly beyond this position to a point where the noseof the part carried thereon engages the resilient stop and moves itoutwardly slightly, approximately as shown in dotted lines in FIG. 8.The spring 222 then causes the slide to retract to the position of FIGIZagain as it moves the shaft 206 in a counterclockwise direction. As theslide retracts, the resilient stop 100 moves to its original positionand nudges the weldable part 24 back to the proper welding position,relative to the chuck.

With the part in proper position and the slide retracted, continuedrotation of the drive shaft 178 cause the welding tool 36 to movedownwardly to the position of FIG. 12. This is accomplished by the firstcam 176 causing the shaft to rotate clockwise and move the lower link136 downwardly, along with the upper link 134. Because of the parallelarrangement of the link pivot pins 130, 132 and 138, 140, the weldingtool 36 remains in a vertical position as it moves downwardly. However,the path of the welding tool is arcuate, as shown in FIG. 12. After theprojection 26 of the weldable part 24 initially contacts the workpiece,at which time the chuck and tool body are inthe positions shown indotted lines in FIG. 12, the welding tool body 40 continues to movedownwardly slightly further and cause the'spring 56 (FIGS. and 6) tocompress slightly as the tool body moves downwardly relative to thechuck leg 42. Atthe same time, the spring 82 for the electrode 88 iscompressed slightly. Because the tool continues to move in the arcuatedownward path between the time the springs 56 and 82 begin to compressand the tool body 40finally stops, the welding part projection 26 andthe electrode tip 88 are wiped or slide across the workpiece slightly,about one-sixteenth inch in practice. This wiping action is important inassuring effective electrical contact between the projection 26 and theworkpiece 20 and also part as the welding tool is raised can alsofacilitate separation of the magnetic chuck and the part.

Because the tabs 24 are often stacked to a considerable height above thefeeding device 38, and because the tabs nest together when stacked, dueto the cooperation of the projectrons 26 and also of the reinforcingrigs 28, it is sometimes difficult to push the lowermost tab forwardlyfrom under the stack by means of the offset 128 of the slide 122. Toovercome this, as shown in FIG. 15, a plunger 238 can clamp a pluralityof the'tabs 24 at an intermediate portion of the stack against theopposite wall 'of the stack passage 124 to enable these tabs to supporttheir weight and the pressure of those thereabove. The relatively fewtabs therebelow then apply relatively little pressure to the lowermosttab when it is engaged by the offset 128 and is moved forwardly by theslide 122.

The plunger 238 is moved forwardly before the slide 122 has moved to itsfully retracted position to clamp the stacked between the electrode tip88 and the workpiece 20. However,

the tool can also be provided with a conventional rectilinear motion, ifdesired.

After the weldable part and the electrode tip 88 come to rest relativeto the workpiece, the second, lift earn 196 comes into operation uponcontinued rotation of the drive shaft 178. Therising portion 198 of thecam 196 pushes the rod 194 forwardly to move the shaft 184 in acounterclockwise direction, as shown in FIG. 4. The lifting ann 182 thenraises the lifting pin 66 and causes the chuck leg 42 and the chuck 62to retract from the workpiece 20. Y I

i The rotor 228 is positioned so that the sector 230 electricallyconnects the contacts 232 and 234 immediately prior to the projection 26of the part 24 leaving the workpiece, so that a pilot arc potential isestablished at this time. Consequently, as the part retracts, a pilotarc is established between the part and the workpiece. As the part movesto or near its retracted position and as the rotor 228 rotates further,the main welding arc is established between the part and the workpieceas the sector 230 connects the contacts 234 and 236.

' The offset 200 of the cam l96'then moves past the rod 194 whichenables the spring 188 to move the shaft 184 in the opposite directionand drop the arm 182, thereby enabling the spring 56 to plunge the part24 and the chuck 62 into contact with the workpiece. The welding arcpreferably is maintained from about the time the plunge starts untilcontact between the projection 26 of the part and the workpiece 20. Thiscan be accomplished by appropriately positioning and designingv theconducting sector 230 and the contacts so that the contabs before theoffset 128 has moved to the rear .of the stack passage. Consequently,when the slide is fully retracted and the offset is to the rear of thestack, the tabs in the lower part of the stack below the plunger 238drop down independently of those clamped by the plunger and those above,with the lowermost one then being ready for engagement by the offset 128upon the next forward movement of the slide 122. The

plunger 238 is retracted clear of the stack, while the offset 128 isforward of the stack to enable the upper part of the stack to dropdownwardly the thickness of one tab before the stack is clamped again.

While the plunger 238 can be driven by a variety of means, as shown, theplunger 238 is held in aguide or track 240 for movement toward and awayfrom the-stack and is urged toward the stack by a spring 242 coiledaround an adjusting rod 244. The rod 244 is screwed into a pivot block246 which is pivoted to a bell crank 248 having a fixed pivot 250. Theother end of the bell crank is connected through an adjusting rod 252 toa lever 254. The lever 254 has an intermediate pivot 256 supported bythe wall of the controller 34 and was has an opposite end engageablewith a cam 258. The earn 258 can be mounted on the shaft 206 whichdrives the linkage arrangement for the slide 122, with the cam 258 beingsuitably shaped to move'the plunger toward the stack against the forceof the spring 242 to providethe above-described movement for the plunger238. I

Various modifications of the above described embodiment of the inventionwill be apparent to those skilled in the art, and

it is to be understood that such modifications can be made tacts for thewelding arc remain closed at least until the stud contacts theworkpiece. If a capacitor power source or similar power source ofgenerally predetermined, short duration is employed, the electricalconnection between the contacts 234 and 236 is'less critical and theycan remain closed long after the stud and workpiece are in contact andthe short power source pulse has dissipated in the electric arc.

After the part is plunged against the workpiece and the projection 26 iswelded to the workpiece, the welding tool is raised from the positionshown in FIG. 14 to the position of FIG. 2, with the welded connectionbetween the part and'the workpiece overcoming the tendency of the magnet90 to retain the part. Hence, when the welding tool. reaches the upperposition, the chuck 62 is empty and is ready to receive another weldablepart. As the welding tool is moved to its.

upper position, suitable means not constituting part of the inventioncan be used to move the next workpiece 20 into welding position underthe chuck.

The slight wiping action between the chuck and the welded withoutdeparting from the scope of the invention, if they are within the spiritand tenor of the accompanying claim.

I lclaim:

w l. apparatus for welding a part to a workpiece comprising means forsupplying power to the part andthe workpiece, means for establishing awelding are between the part and the workpiece and a welding toolincluding a body, a chuck leg carried for. longitudinal movement in saidbody and having an end extending from said body, spring means urgingsaid leg out of said body and toward the workpiece, a chuck for holdinga part connected to said leg, means for retracting said leg and saidvchuck when in a position in which a part carried by said chuck is incontact with the workpiece, said retracting means comprising a camhaving a sharp offset, means including a driveshaft for rotating saidcam, lifting means including a push rod, having a free terminal end,engaged by a drive arm driven by a shaft, the shaft connected to a liflarm for rising

1. An apparatus for welding a part to a workpiece comprising means forsupplying power to the part and the workpiece, means for establishing awelding arc between the part and the workpiece and a welding toolincluding a body, a chuck leg carried for longitudinal movement in saidbody and having an end extending from said body, spring means urgingsaid leg out of said body and toward the workpiece, a chuck for holdinga part connected to said leg, means for retracting said leg and saidchuck when in a position in which a part carried by said chuck is incontact with the workpiece, said retracting means comprising a camhaving a sharp offset, means including a drive shaft for rotating saidcam, lifting means including a push rod, having a free terminal end,engaged by a drive arm driven by a shaft, the shaft connected to a liftarm for rising the chuck leg when the free terminal end of the push rodcontacts a relatively sharply rising portion adjacent the offset, thechuck leg and the chuck being plunged abruptly back toward the workpieceby the spring means when the push rod drops over the offset.